Recent progress in ultra-low power (ULP) circuit design has been made due to significant interest in environmental and biomedical sensor applications. These systems often include analog and mixed-signal modules such as linear regulators, A/D converters, and RF communication blocks for self-contained functionality.
Voltage references (VR) are key building blocks for these modules. In particular, linear regulators require a voltage reference to supply a constant voltage level to the entire system. Also, amplifiers in A/D converters employ several bias voltages. Therefore, it is often necessary to incorporate multiple voltage reference circuits in a system.
Voltage references are commonly integrated in wireless sensing systems with tight power budgets, which are often less than hundreds of nanowatts due to very limited energy sources. Hence, it is vital that voltage references consume very little power. On the other hand, voltage references should be able to operate across a wide Vdd range, in particular near or below 1V, since some power sources, such as energy scavenging units, provide low output voltages.
This section provides background information related to the present disclosure which is not necessarily prior art.